An Ethernet Virtual Private Network (EVPN) is a network service that provides Ethernet connectivity for two or more remote layer two (L2) local area networks (LANs) through an intermediate layer three (L3) network (usually referred to as a provider network), in a transparent manner, i.e., as if the intermediate L3 network does not exist. In particular, an EVPN transports L2 communications, such as Ethernet packets or “frames,” between remote networks via the intermediate multiprotocol label switching (MPLS) network. In a typical configuration, provider edge (PE) network devices (e.g., routers and/or switches) of the intermediate networks coupled to the customer edge (CE) network devices of the customer networks define label switched paths (LSPs) (also referred to as pseudowires) within the intermediate network to carry encapsulated L2 communications as if these customer networks were directly attached to the same local area network (LAN).
A provider backbone bridged (PBB) EVPN combines EVPN services as well as MAC-in-MAC encapsulation when transporting L2 communications. That is, each customer frame transported through the PBB-EVPN utilizes MAC-in-MAC encapsulation in which customer MAC (C-MAC) addresses within the header are encapsulated within backbone MAC (B-MAC) addresses, thereby maintaining separation between the provider L2 domain and the customer L2 domain.
In a PBB-EVPN, a set of PE devices may operate in a common Ethernet segment in active-active mode with all PE routers forwarding network traffic in the Ethernet segment. One of the PE devices in the Ethernet segment may operate as a designated forwarder (DF) to forward Broadcast, Unknown unicast, and Multicast (BUM) traffic while the other PE devices, e.g., non-designated forwarders (non-DFs), in the Ethernet segment drop BUM traffic. The Ethernet segment may also be associated with a B-MAC address, which is used by remote PE devices to forward network traffic through a service provider network to the set of PE devices included in the common Ethernet segment.